1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a filter module, and more particularly to a multi-band filter module available in various frequency bands and a method of fabricating the multi-band filter module.
2. Description of the Related Art
Recently, as telecommunication appliances represented by mobile phones are rapidly popularized, demand for a thin and light filter for use in these appliances also increases.
In particular, as the telecommunication appliances are miniaturized and become more complicated, there is a need for a small-sized terminal able to utilize multiple frequency bands. In order to utilize multiple frequency bands, a multi-band filter is acutely needed, which filters only required frequencies among signals received through one antenna. An existing method of implementing a multi-band filter using of a ceramic filter has weak competitiveness in comparison with an Film Bulk Acoustic Resonator (FBAR) or a Surface Acoustic Wave (SAW) device in view of its size and properties.
Up to now, the smallest device having a good frequency characteristic in the 2 GHz band is the FBAR using the bulk acoustic characteristic, while the smallest device having a good performance in the 900 MHz band is the SAW device using the surface acoustic characteristic.
The FBAR has the advantages of mass production and miniaturization. Also, the FBAR has a high quality factor that is a major property of a filter, and can be used in a micro frequency band, in particular, in the Personal Communication System (PCS) band and a Digital Cordless System (DCS) band.
The FBAR is generally fabricated by sequentially depositing a lower electrode, a piezoelectric layer, and an upper electrode on a substrate. According to the operating principle of the FBAR device, electric energy is applied to the electrodes to induce an electric field in the piezoelectric layer that is temporally varied, and then the electric field causes a bulk acoustic wave in the same direction as a vibration direction of a resonant part in the piezoelectric layer to generate resonance therein.
Both the FBAR and the SAW device utilize the RF characteristic using the acoustic resonance. However, the SAW device can obtain a good characteristic only by using a specific piezoelectric substrate. In the case of the FBAR, although it is not limited to a substrate, a silicon substrate is generally used so as to be inexpensive, integrated, and compatible with IC.
A common multi-band filter is generally fabricated by separately making the above filter devices and combining the filter devices with chips and trimming circuits through additional packaging. The method of fabricating the multi-band filter using a separately made filter has a complicated construction, many defective factors such as short circuits, and an increased size.
Accordingly, a need exists for a development of a multi-band filter module having a thin and simple construction and fabricated by a simple method.